This invention relates generally to radar systems, and more specifically to a radar system which is capable of determining the phase angle of radar return signals.
The proper navigation of an aircraft in all phases of its flight is based to a large extent upon the ability to determine the terrain and position over which the aircraft is passing. Pulse radar altimeters accurately determine altitude using leading edge return signal tracking. Specifically, a pulse radar altimeter transmits a pulse of radio frequency (RF) energy, and a return echo is received and tracked using a tracking system. The interval of time between signal bursts of a radar system is referred to as a pulse repetition interval (PRI). The frequency of bursts is referred to as a pulse repetition frequency (PRF) and is the reciprocal of PRI.
A radar altimeter mounted on an aircraft transmits a signal that impinges a ground patch bounded by an antenna beam. Radar return signals are typically out of phase with the transmitted radar signal. A method for determining the phase angle of a radar return signal in an interferometric radar system has been previously described. In this method the computed values are filtered in order to improve signal-to-noise ratio. However, such filtering adds latency to the radar altimeter system, and does not take advantage of information available in the original signal.